The invention relates to a method for soldering or brazing components made of aluminium or aluminium alloys using aqueous flux preparations selected from the group consisting of potassium fluorozincate, cesium fluorozincate, cesium fluoroaluminate, and especially potassium fluoroaluminate, and also mixtures thereof.
It is known to braze together components made of aluminium or aluminium alloys using aqueous preparations of fluxes containing potassium fluoroaluminate. The purpose of the flux is to remove interfering oxide layers on the degreased components, in order to permit satisfactory brazing. To this end, an aqueous preparation of the potassium fluoroaluminate can be used, which is applied to the component or components, for example by spraying, dipping the workpieces into the aqueous preparation, coating the workpieces, etc. The components are then brought into contact at the points which are to be brazed together, and heated. First the water of the suspension evaporates, then the flux melts. Finally, there is formed from braze material or solder, which is either added or produced in situ, a eutectic of solder and aluminium or aluminium alloy which produces the brazed joint. Usually, an excess of the flux preparation is used. Consequently, the excess aqueous preparation of the potassium fluoroaluminate flux is recovered and re-used. This applies, in particular, when the components are applied by spraying. The proportions of flux and water in the recirculated preparation are adjusted to a predetermined value by the addition of flux or water. After a predetermined time, for instance in the evening or after the end of a shift, the spent preparation is not used any further. Instead, a fresh preparation is produced and used. The preparation which is no longer used is a waste water which contains flux and, due to the solubility of the fluorine-containing flux, has a high fluoride content. Such a waste water is also produced if apparatus and operating parts used in the brazing process are cleaned after a predetermined period of time. Such waste water has hitherto been discharged into the environment more or less untreated.